Some of the major Unix commands used in day to day work:
- logname ->displays current user name
- hostname ->displays host name
- -i to display ip address (io) (/sbin/ifconfig -> to display internet ip address)
- who ->displays all logged users; tells you who’s logged on and login time
- whoami ->displays current user; returns user name
- uname ->uname prints system information
-a -> all information (-s -> kernel name, -r -> kernel release, -n -> node name, -v -> kernel version, -m -> machine hardware name, -p -> processor type or unknown, -o -> operating system, -I -> hardware platform)
- exit ->logs out from current user
- clear ->clear the terminal screen
- pwd ->print name of current/working directory
- passwd ->lets you change your password
- date ->Displays current date time
Format: Mon Mar 21 15:32:20 EDT 2011
date +%m -> displays month from the date
%d -> day of months (1-31)
%m -> month in two digits
%y -> last two digits of year
%Y -> four digits year
%H -> hours (0..23) 24 hour format
%M -> Minutes
%S -> Seconds
%D -> Date; same as %m/%d/%y
%T -> only time part from current date
- cal->displays calendar for current month
eg: cal 01 2010 <displays jan-2010 calendar>
cal 2011 – displays 2011 year calendar
cal -3 -> displays calendar for previous, current and next months
- printenv
prints environment variable values
$ printenv EDITOR USERNAME ….. ->prints the values of environment variables listed
If no variables are specified, printenv prints the value of every environment vairable.
- echo -> echo prints given string;
echo is also use to print the value of environment variable when specified with $;
eg:printenv EDITOR = echo $EDITOR
some of the environment variables are: HOME, USER, PATH, TERM, MAIL, EDITOR
$ echo My present working directory is `pwd` -> outputs
( ` -> Acute/Back quote symbol helps to concatenate the command output with text )
My present working directory is /home/Temp
- man ->$man echo -> provides help on unix command echo (displays manual)
- ls-> displays files and directories order by name
ls -x -> width wise
ls -l -> displays long list of files and directories order by name
ls -r -> reverse order of file name
ls -t -> order by timestamp (latest first)
ls -lrt -> order by timestamp (oldest -> latest)
ls -a -> displays hidden files also
ls -R -> displays list of files and directories recursively (including sub directories contents)
ls *.* -> displays all files with any extensions
ls p* -> displays only files starting with character ‘p’
ls a* -> lists all the files starting with character ‘a’
ls *e -> lists files ending with character ‘e’
ls -d */ -> displays only directories from present working directory
Wild Card Characters
* -> combination of zero or more characters
? – represents single character
[..] ->any character from the list
[!..] ->other than characters specified in the list
– ->used to specify range
- chmod->The chmod command (abbreviated from change mode) lets the user change the permissions of files and directories.
There are many ways by which UNIX permission schemes are represented. The most common form is symbolic notation
ls -l prints symbolic notation for files and directories
The first character indicates the file type:
– denotes a regular file
d denotes a directory
b denotes a block special file
c denotes a character special file etc.,
Each class of permissions is represented by three characters
– The first set of characters represents the user class
– The second set represents the group class
– The third and final set of three characters represents the others class
Each of the three characters represents the read, write, and execute permissions respectively
r if the read bit is set, – if it is not
w if the write bit is set, – if it is not
x if the execute bit is set, – if it is not
The following are some examples of symbolic notation:
-rwxr-xr-x for a regular file whose user class has full permissions and whose group and others classes have only the read and execute permissions
crw-rw-r– for a character special file whose user and group classes have the read and write permissions and whose others class has only the read permission
dr-x—— for a directory whose user class has read and execute permissions and whose group and others classes have no permissions
u represents user
g represents the group
o represents others
a represents all
r represents read
w represents write
x represents execute
+ -> to add a permission
– -> to remove permission
= -> to assign permission
chmod g=rwx sample.txt
chmod g=r_x sample.txt
chmodugo=rwx sample.txt
chmodg+rwx,u+rwx,o+rwxsample.txt
Access rights to directories
r -> allows to list files in the directory
w -> user may delete files or move files into it
x -> right to access the files; If you have ‘x’ for the directory then you can read a file in it
r -> 4; w -> 2; x -> 1
octal digit values:
0 — no permission
1 –x execute
2 -w- write
3 -wx write and execute
4 r– read
5 r-x read and execute
6 rw- read and write
7 rwx read, write and execute
chmod 537 sample.txt to give read/execute to the user, write/execute to the group, read/write/execute to others
Usually, UNIX administrator takes care of changing owner and group of a file
- touch -> used to create new 0 byte file(s)
$touch file1.txt file2.txt -> creates two 0 byte files with names file1.txt and file2.txt
-t option in touch command is used to change the timestamp of an existing file or to create a new file with the different timestamp
$touch -t 201201081145 file1.txt -> file1.txt timestamp will be changed to Jan 8 2012 11:45am
$ touch –t 201202191345 newfile.txt -> newfile.txt created with Feb 19 2012 1:45pm timestamp
- cat ->to display contents of an existing file or to create a new file
Existing:
$cat type1.txt -> displays contents of type1.txt
$cat type1.txt type2.txt type3.txt -> displays contents of type1.txt followed by contents of type2.txt followed by contents of type3.txt
New:
$cat >type3.txt
SCD type3 stores partial history
<Ctrl+d>
$cat type1.txt type2.txt type3.txt >type.txt -> contents of type1,type2,type3 will be stored in type.txt
$cat type1.txt >> abc.txt -> appends the contents of type1.txt to abc.txt
- more -> displays page full of file content
enter -> next line; space -> next page; q -> quit;
- mkdir -> to create new directory/directories
$mkdir dir1 dir2…. dirn
- cd ->command used to change the directory
cd<dir> change directory
cd .. Change to parent directory
cd\ change to root directory
cd – will change prompt to previous path
tab -> will give full name of file if starts typing;
eg: type sr and then press tab -> displays all the files starting with sr
- cp -> copies files and directories
cp<f1><f2> -> copies f2 with same content as f1
cp -i file1 file2 -> if file2 already exists, then asks for confirmation to overwrite
cp -p -> to copy with same timestamp
- rmdir -> command to remove an empty directory
- rm -> removes files or directories
rm -i -> asks for confirmation before deleting
rm -r -> to remove directory with contents
rm*.* -> removes all files with extensions
- mv ->to rename a file/directory
mv f1 f2 -> to rename a file f1 to f2
$mv sample .sample -> makes sample as hidden file
> -> Output redirection
>> -> append redirection output
< -> input redirection
; -> is a command separator – it helps to execute more than one commands separated by ;
| ->redirects the output to next command
- head -> command used to display top n lines from an existing file
$ headsample.txt -> displays top 10 lines from file sample.txt
$ head -5 sample.txt -> displays top 5 lines/rows from file sample.txt
- tail -> command used to display bottom n lines/rows from an existing file
tail student -> displays last 10 lines/rows from file student
tail -5 student -> displays last 5 lines/rows from file student
head -15 student | tail -5 -> displays from 11th to 15th records from file student
tail -f rel355load.log -> (-f follow)output appended data as the file grows)
- wc ->print the number of newlines, words, and bytes in files
wc -l filename ->print the new line count in the file
wc -w filename -> displays word count in the file
wc-c filename ->print the byte count in the file
- grep ->grep stands for -> globally search regular expression and print
grep ‘abc’ sample.txt ->displays all lines having abc from file sample.txt
-w ->searches for ‘abc’ as the whole word and not part of another word
-v ->displays non-matching lines
-i -> ignore case when searching
-r -> searches in all files under folder recursively
-n ->prints line numbers as well
-c ->to print only the total count of matched lines
-o ->Show only the part of a matching line that matches search pattern
-l -> list files having the search string
-L -> list files not having search string
^ -> to specify line starting with specific pattern
grep ‘^abc’ sample.txt displays lines that start with abc in file sample.txt
$ -> to specify line ending with specific pattern
grep ‘abc$’ sample.txt displays lines that end with abc
grep ‘^abc$’ sample.txt displays lines that contain only abc
grep ‘^$’ sample.txt displays blank lines
grep ‘^..$’ sample.txt displays lines with only two characters
ls -l | grep ‘^d’ -> displays directories from present working directory
ls -l | grep ‘^-‘ -> displays regular files from the present working directory
- find ->The find command searches through the contents of one or more directories, including all of their subdirectories. You have to tell find in which directory to start its search;
find . -name abc.txt -> searches for files with name abc.txt under current directory including subdirectories
$find -newer file1 -> displays files newer than file1
$find . -name ‘h*’ -> displays files starting with h in current directory including sub-directories
$ find . -name ‘D*’ -type f -> displays only files starting with D
$ find /home/Temp/new -type f -name “h*” ->searche for only files starting with h in /home/Temp/new including subdirectories
$ find /home/Temp -path /home/Temp/new -prune -o -type f -name hello -> displays all the files with name hello found in /home/Temp excluding /home/Temp/new
$ find /home/Temp -type d -name “abc*” -> displays only directories starting with abc in /home/Temp and subdirectories
$ find .\( -name “*.txt” -o -name “*.dat” \) -type f -ls ->searches for files with extension .txt or.dat and displays as long list
find . -mmin -4 -print -> displays all the files/directories modified within last 4minutes
find . -mmin +4 -print -> displays all the files/directories modified at least 4minutes back
-mmin -> modified -amin -> accessed
find . -mtime +30 -ls -> lists all the files/directories modified at least 30days back
find . -mtime +30 -prints -> prints files/directories modified at least 30days back
$find . -size 0 -> displays 0-byte files along with path starting current folder
$find . -empty -type f -print -> to print only empty files
$find . -empty -type d -print -> to print only empty directories
$find . -empty -print -> to print empty files and directories
$find . -size +500c -print -> prints all the files with more than 500 characters in size
- cut ->Print selected parts of lines from each FILE to standard output. Popular usage is to get required columns from a delimited file.
-c -> select only these characters
-d -> to specify the delimiter
-f -> to specify the field list
-s ->do not print lines not containing delimiters
$cut -c2,4-5 student -> prints 2nd, 4th to 5th characters from file student to standard output
$cut -d ‘;’ -f 1,3filename -> cuts columns 1 and 3 from file (delimiter is semicolon) – which is specified using -d; if you do not specify any delimiter – Unix assumes delimiter is tab
- sort -> sort command prints the content of a text file in sorted order. Sorting is done based on one or more sort keys extracted from each line of input. By default, the entire input is taken as the sort key.
-r -> outputs in reverse order
-n -> option makes the program sort according to the numerical value (eg: if we have 1001, 110 normal sort will display 1001 first and then 110, but when used -n, 110 is displayed first and then 1001)
-t -> to specify delimiter when sorting a delimited text file
-k -> to specify a key (or range of keys) to sort
-f -> to ignore case
-c ->check whether the input is sorted; do not sort (output not displayed when the input is sorted; else print the location of disorder)
$sort file1 > file2 -> sorts the contents of file1 and redirects the output into file2
sort -k4 <filename> -> sorts the contents of file with respect to 4th column
sort -k4 -k2 <filename> -> sorts the contents of file by 4th column and then by 2nd column
sort file1 –o sfile -> sorts files file1 and redirects the output to sfile instead of standard output
$ sort -t’|’ -k2<filename> -> to sort a pipe-delimited file based on second column
- uniq ->uniq is a Unix utility which, when fed a text file, outputs the file with adjacent identical lines collapsed to one. It is a kind of filter program. Typically it is used after the sort. It can also output only the duplicate lines, or add the number of occurrences of each line etc.,
*provide sorted input*
uniq filename -> outputs file content with adjacent identical lines collapsed to one.
uniq -c filename -> also adds the number of occurrences of each line (-d -u are ignored when used -c)
uniq -u filename -> displays only non-duplicate rows
uniq -d filename -> displays only duplicated rows
-i -> ignore case when comparing lines
eg: sort filename | uniq -ui
-f ignores the number of fields (A field is a run of whitespace, then non-whitespace characters.
sort -k4 uniq_demo1 | uniq -f3 -> sorts file based on 4th column and redirects the output to uniq -f3 command (uniq -f3 ignores first 3 columns and displays the output considering only data after 3 cols)
-s ->skips the number of characters in a line
-w -> compare no more than specified characters in each line.
- cmp ->compares both the files and gives no output in case both the files are equal. It returns the location of first difference when files are unequal
- diff -> this command displays the difference between two files; If there are no differences between the files, you will see no output, but if two text files are indeed different, all the text mismatches will be highlighted using the standard diff output:
d (deleted) -> denotes record is not present in file2
c (changed) -> denotes record in file1 is different from file2
a (added) -> denotes record is present in file2
< denotes content from file1
> denotes content from file2
< will be displayed in case of d
<and> will be displayed in case of c
> will be displayed in case of a
- comm ->compare two sorted files line by line and produces three-column Column one contains lines unique to FILE1, column two contains lines unique to FILE2, and column three contains lines common to both files.
-1 suppress lines unique to FILE1
-2 suppress lines unique to FILE2
-3 suppress lines that appear in both files
- gzip -> reduces the size of the named files and each file is replaced by one with the extension .gz, while keeping the same ownership modes, access and modification times, gzip will only attempt to compress regular files.
$ gzipsample -> produces filesample.gz
- gunzip ->gunzip takes a list of files on its command line and replaces each file whose name ends with .gz
$ gunzipsample.gz ->uncompressessample.gz and produces file sample
- zcat ->Once the file has been compressed, we cannot view it using the normal cat command. Unix provides a utility zcatto view the contents of a compressed/zipped file.
$zcat sample.gz -> displays file contents in readable format
- sleep ->sleep helps to delay for a specified amount of time
sleep 20 -> delays for 20 seconds which is same as sleep 20s
also, we can use m or h m-> minutes, h-> hours
eg: sleep 3m -> delays for 3 minutes
- ps ->ps selects all processes with the same effective user ID as the current user and associated with the same terminal as the invoker. It displays the process ID (pid=PID), the terminal associated with the process (tname=TTY), the cumulated CPU time in [dd-]hh:mm:ss format (time=TIME), and the executable name (ucmd=CMD). The output is unsorted by default.
ps -e -> to display all processes
ps -u <username> -> lists processes related to specific user
- kill -> to terminate a process
kill PID -> kills the process with specified PID
kill -9 <jobid> -> force kill the process
- fg -> command helps to get the background process to foreground
$ fg % processid -> gets process to foreground
- bg ->Resume each suspended job in the background
This command helps you to change the foreground process to background process, once we start any process in foreground we can press ctrl+z to stop it and once you see $ prompt we can type bg which resumes that process as background process
- nohup ->nohup is a command to ignore the HUP (hangup) signal, enabling the command to keep running after the user who issues the command has logged out. nohup is most often used to run commands in the background. The output that would normally go to the terminal goes to a file called nohup.out if it has not already been redirected. This command is very helpful when there is a need to run numerous batch jobs which are inter-dependent.
nohup is a low-level utility simply configuring a command to ignore a signal
eg:
$ vi a.sh
#!/bin/bash
echo ” Starting Script”
sleep 15
echo ” in middle of script”
sleep 15
echo “done”
a.sh takes atleast 30 seconds to complete
$ nohupsh a.sh& (executing a.sh as background process)
exit (immediately)
The output of the above job is appended to existing nohup.out file or will create a new file nohup.out and redirect the output of process/job.
Once you exit from the terminal and then re-login and check nohup.out – you can see that process got completed though we logged out without waiting for job completion.
- mail ->mail is a command line email client for Unix and Unix-like operating systems
-s -> lets you give subject (eg: -s “Hello”)
-c -> lets you give an email address to be cc’ed (if more, separated by comma)
-b -> lets you give an email address to be bcc’ed (if more, separated by comma)
-a -> lets you send the file as an attachment
$ mail -s “Test Email” -c [email protected] -b [email protected] [email protected] abc.txt
above command will
send an email to [email protected]
cc to [email protected]
bcc to [email protected]
subject -> Test Email
the body of the email -> contents of file abc.txt
to send abc.txt as an attachment -> please specify -a abc.txt
- split -> helps to output fixed-size multiple files of a given input file
Default size is 1000 lines and default PREFIX is ‘x’
Assume sample has 2384 lines
$ split sample -> generates 3 files
xaa (with 1000 lines); xab (with 1000 lines); xac (with 384 lines)
$ split -d sample -> generates 3 files
x00 (with 1000 lines); x01 (with 1000 lines); x02 (with 384 lines)
$ split sample samp-> generates 3 files
sampaa (with 1000 lines); sampab (with 1000 lines); sampac (with 384 lines)
-b1000 -> outputs files each with 1000 bytes size
-l500 -> l stands for lines -> outputs files each with 500 lines
-a ->use suffixes of length N (default 2)
- ftp -> FTP is the user interface to standard File Transfer Protocol. The program allows a user to transfer files to and from a remote host/network site.
- lcd ->Change the working directory on the local machine
- lpwd / !pwd -> display current working directory on local machine
- put ->Store a local file on the remote machine
- get ->Retrieve the remote-file and store it on the local machine
- bye ->Terminate the FTP session with the remote server and exit ftp
- sed-> stream editor— Helps in Find and Replace action
sed -n 10p numbers.txt -> prints 10th line
sed -n 10,20p numbers.txt -> prints line 10 to 20 in numbers.txt
sed 5d numbers.txt -> prints file numbers.txt except line 5
sed s/abc/def/ abc.txt -> replaces abc with def in file abc.txt (but only first occurance in each line – replaces in all lines but only first occurance)
sed s/is/was/g today -> replaces every occurance of ‘is’ with ‘was’ globally in file today and displays as output – it will not replace the contents of the original file
sed “s/A/a/g;s/N/n/g” dept -> A is replaced with a and N is replaced with n in a file dept
Please use ‘>’ and new file name to redirect the output to a new file – as original file content is not changed using sed
s -> stands for substitute
g -> stands for global
/ -> delimiting symbol
I can create a file called changes.txt with below content
s/a/A/g
s/b/B/g
s/is/was/g
and use $ sed -f changes.txt today
displays today file contents with all the changes – but ‘a’ in ‘was’ is not displayed as capital letter
sed ‘/^$/d’ today -> deletes empty lines from file today and displays – no changes made to actual file
sed ‘/ /d’ today -> deletes any line with space and displays
sed ‘/e$/d’ today -> deletes line(s) ending with e and displays
sed ‘/^ *$/d’ today -> blank lines or lines with spaces only are deleted in display
sed ‘/is*/d’ today -> deletes lines with occurance of is
$echo day | sed ‘s/d/(&)/’ -> outputs (d)ay; & represents search string
sed ‘s/word1/word2/g’ input.file
sed ‘s/word1/word2/g’ input.file > output.file
sed -i ‘s/word1/word2/g’ input.file
sed -i -e ‘s/word1/word2/g’ -e ‘s/xx/yy/g’ input.file
vi editor commands
esc -> command mode
i ->enter into insert mode – can start inserting characters
shift + i ->move to the beginning of the line and enters into insert mode
a ->enter into insert mode – can start inserting characters from next character to cursor
A -> start appending at end of the line
x -> to delete a character under the cursor
X -> removes character prior to cursor (which works like backspace)
o -> insert an empty line below the current line
O (shift + o) -> insert an empty line above the current line
cc ->copy and clear text in current line without deleting the line
yy -> copy current line
y$ ->copy from cursor till the end of the line (including the character under cursor)
y0 (zero) ->copy from the beginning of the line till cursor (including the character under cursor)
yw ->copy from cursor till the beginning of next word (including the character under cursor)
yb ->copy from the beginning of the word till cursor (excluding the character under cursor)
p -> paste copied line below the current line
P (shift + p) -> paste copied line above the current line
dd -> delete current line (5dd deletes five lines including current line and following 4 lines)
dw ->deletes current word in the forward direction
db ->delete the current word on backward direction
d$ ->deletes current line from cursor position until end of the line
d^ ->deletes the current line from the beginning of the line till character before cursor(current) position
h -> moves cursor left
j -> moves the cursor down
k -> moves the cursor up
l -> moves cursor right
:w -> to save a file
:q -> to quit
:q! ->force quit (quit without saving)
:wq -> save and quit
:= -> total number of lines in file displayed at bottom the screen
:.= -> current line number
:set nu ->sets the line numbers for a file
:setnonu -> removes line numbers
H -> moves to top of the screen
M -> moves to middle of the screen
L -> moves to bottom of the screen
G ->Moves to the last line in the current file (end of file)
:w file1 -> save as file1 -> to save current file as file1 -> without removing original file
/string -> searches for a string in the forward direction
?string -> searches for a string in reverse direction
n -> next occurrence in search direction
N ->previous occurrence in search direction
Disclaimer:
This article is written solely for the information purpose. The author has collected information from various websites for some of the answers and some of the answers (Not All) might be a direct copy and paste.
The article was collected and written by Bijaya Subedi. Bijaya is currently working as an ETL tester in a DC/VA based Mortgage Company.
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